1. Field of the Invention
The present invention relates generally to medical therapeutic systems, and deals more particularly with methods and devices for treating and curing functional disorders of the human carpus. More particularly, the present invention provides a splint for providing dynamic pressure to the transverse carpal, volar carpal, and intra-carpal ligaments, in a manner tending to relieve contractures of these ligaments and thus relieve the pain caused thereby.
2. Description of the Related Art
A. General Description of the Condition
Carpal tunnel syndrome (CTS) is a painful condition caused by compression of the median nerve of the forearm. The median nerve and the flexor tendons pass from the forearm to the hand through the wrist canal, or carpal tunnel. The median nerve in particular can be compressed by one or more factors such as a reduction in carpal tunnel volume or swelling of tissues passing through the carpal tunnel. Such compression of the median nerve causes intense pain to the patient, often necessitating extended therapy or surgery to alleviate the problem.
It is commonly believed that CTS is caused by prolonged repetitive activity, such as holding the hand, wrist, and forearm in an awkward position for extended lengths of time while exerting the associated muscles. Prolonged exertion at a keyboard or manual labor are common, but by no means the only, associations with CTS. The direct cause of CTS is believed to be a biomechanical ligament imbalance in the volar carpal ligaments, where the term xe2x80x9cvolarxe2x80x9d indicates a direction towards the palm of the hand as opposed to xe2x80x9cdorsalxe2x80x9d which indicates a direction towards the back of the hand. Specifically, this biomechanical imbalance of the ligaments is believed to comprise a thickening of the palmer transverse carpal ligament (PTCL, also known as the retinacular ligament), a thickening of the volar intracarpal ligaments, and contraction of an assortment of volar carpal ligaments.
B. Kinematics of the Carpal/Forearm Complex
The flexor muscle tendons of the forearm acting on the wrist, fingers, and thumb volarly exert a collective static force many times greater than the extensor muscle tendons acting dorsally to stabilize these same members. This interaction between the flexor muscles (antagonist) and the extensor muscles (agonist) is termed xe2x80x9ccocontractionxe2x80x9d. Cocontraction tends to hold the joint in a fixed and stable position. The flexor-to-extensor ratio of these opposing forces is normally four to one. However, work demands often increase this ratio through hypertrophy of the flexor muscle tendon units; this hypertrophy is caused by executing high intensity tasks involving extended duration and which dominantly involve finger, thumb, and wrist function.
The interaction between the carpal ligaments and the flexor and extensor muscles becomes more pronounced with time and intensity of activity. The effect of the volar flexor forces, acting upon the PTCL as a pulley, attenuate the PTCL and apply forces anteriorly and medially. This places traction forces to the ligament ends of the carpus. Each night, while the flexor/extensor muscles are at rest, the volar intracarpal ligaments restore their normal position grossly; however, some minute anteriomedial deformity remains, and slack of the PTCL is concurrently taken up by contractile forces of this and the other ligament(s). Numerous cycles of activity followed by rest develop an established deforming characteristic which is manifested by narrowing the horseshoe ends of the carpal tunnel, which are held in position by a thickening PTCL and other volar carpal ligaments, resulting in a transverse deformity. Simultaneously, the PTCL, acting as a pulley, concentrates the load of the finger and thumb function so that a volar glide is initiated, where volar glide is defined as movement of the carpal metacarpal complex as a unit in a volar direction. This volar glide of the carpal metacarpal complex attenuates the predisposed thin dorsal carpal ligaments (DCL) originating from the distal radial ulna (DRU). Since the volar carpal ligaments collectively become less stressed, they begin to contract, thus encouraging the anteriomedial collapse of the intercarpal spaces simultaneous to a longitudinal deformity.
The long moment arm of the carpal muscle tendon units are only capable of stabilization of the carpus when the muscle tone is within normal limits, i.e. flexor-to-extensor ration of approximately 4 to 1; these forces acting on the carpus in flexion are convergent toward the muscle origin and are regulated by an interplay of antagonists, pulleys, and joint alignment. A variation of one or more serves to simplify convergence towards a direct line to this point of origin and shorten the distance therebetween. This force results in a decreasing biomechanical advantage which is manifested by a volar shift of the axis of the proximal carpal row. This may account for the propensity of patients with CTS to develop odd compensatory behaviors as, for example, flexing the wrist during power grasping, conceivably to account for the change in position of the more volarly placed PTCL. Carpal tunnel volume is further reduced, and any other predisposition will hasten onset of the painful and crippling CTS condition. Thus, the resistance of the PTCL and related volar ligaments which is encountered when returning the carpal metacarpal complex to a neutral position, i.e. dorsal glide, should be indicative of the severity of the condition of carpal tunnel syndrome or the propensity of the subject to incur the condition.
C. Standard Treatment of Carpal Tunnel Syndrome
To date, CTS has been treated with wrist rests, anti-inflammatory medications, cortisone injections, surgery, and static and dynamic wrist splints. Alone or combined, these treatments have met with varying degrees of minimal success. Symptom relief is short lived and compounded by surgical complications. Even after these treatments are applied, the patient""s biomechanical configuration remains unchanged or complicated. Reduced grasp strength has been well documented. The obvious solution, i.e. removing the cause of the injury by refraining from the manual labor believed to cause the problem, is not always practical since the cause of the injury is frequently the means by which the patient obtains his or her livelihood. The next best choice, prevention through proper intervention, can be achieved by enlarging the carpal tunnel to maintain adequate space for the median nerve and thus avoid compression. However, the mechanism for correcting this condition long term does not yet exist.
The carpal tunnel can be enlarged by osteopathic manipulation and stretching maneuvers, thereby alleviating compression on the median nerve and resolving CTS. While severe cases may require other treatment, manipulation is effective in the majority of cases and has the advantage of being prophylactic, i.e. a preventative. Optimum resolution of the symptoms requires frequent stretching and the assistance of another person, a physician or therapist to perform the manipulation. There is a need for an appliance which a patient can use to augment treatment by the physician or therapist. It is known from studies of rehabilitated knee joints and elbow joints that the longest period of low force stretching produces the greatest amount of permanent elongation of connective tissue. Ideally, the stretching would be accomplished by means of an appliance which is adjusted by the physician or therapist to provide the appropriate force for stretching, preferably continuously.
The prior art is replete with splint appliances which are designed to reduce CTS pain. One such appliance is described in U.S. Pat. No. 5,417,645, issued to Lemmen, where a carpal splint is provided with an elongated, flexible member having a palmar portion configured to extend from the middle of the forearm, across the volar carpal area, and across the palm to bias the palm in a dorsal direction. It also functions as a reminder of the proper positioning to relieve pressure on the median nerve associated with CTS. It is designed to allow use of the fingers and thumb and to permit near normal hand function.
Another such appliance is described in a series of patents by Davini, i.e. U.S. Pat. Nos. 4,966,137, Re. 34,627, and 5,385,527. Each of these appliances is based upon essentially the same premise, namely, each functions to enlarge the carpal tunnel by compressing the radius and ulna together using an external clamp and bandage configuration which encircles the carpus, so that free use of the hand and fingers is permitted. Stretching of the PTCL or other carpal ligaments is not addressed by these devices.
Still another such appliance is described in U.S. Pat. No. 5,468,220, issued to Sucher. Like the ""137 and ""627 patents, it is also intended to relieve pressure on the median nerve by increasing the volume of the carpal tunnel. The appliance encircles the carpus and, using spring loaded pads, provides dorsal and volar pressure on the radius, ulna, and other carpal bones which tends to increase tunnel volume. It can be removed by the user if long term use causes irritation or sensitivity to the skin.
However, there are a number of difficulties in the use of such appliances. First, simply prescribing the use of an appliance does not mean that the patient will use it properly. If a patient is expected to put on and remove an appliance, a properly adjusted appliance must not be able to be put on incorrectly or to inflict either too much or too little stretching. Proper use also refers to the compliance or self-discipline of the patient and how easy it is to use the appliance. In general, an appliance that is mechanically simple, easy to use, and comfortable to wear will more likely be used as directed.
Second, the skin is sensitive to long term pressure, which can cause a localized loss of circulation and lead to ulceration. Obviously, a patient will not be comfortable if an appliance causes such irritation. On the other hand, sufficient pressure must be applied in order to be effective. Such an appliance must be comfortable to wear and not cause undue irritation or pressure on the skin.
Third, an appliance must not interfere with the normal activities of living. It must be comfortable in the sense that it does not interfere with the function of the arm, wrist, and hand. Otherwise, a patient is unlikely to wear the appliance long enough to be fully effective, preferably overnight, or when performing routine tasks which may irritate the median nerve or promote the deformities. An appliance duplicating the manipulation by a physician or therapist would obviously interfere with the patient""s use of the hand. What is desired is an appliance which duplicates as much of the physician""s treatment as possible without interfering with the use of the arm, wrist, or hand.
Fourth, it is desirable to have an appliance which will not only promote the stretching of the carpal ligaments so as to relieve pressure on the nerve, but also to restore the proper ratio of cocontraction between the flexor and extensor muscles which tend to hold the carpal joint in the proper alignment while carpal ligament stretching is being effected. This encouragement of cocontraction is missing from all existing devices. In order to achieve proper joint stabilization, the device must allow the ligaments to re-engage and reestablish joint stability as well as increasing muscle tone of the flexor and extensor muscles around the perimeter of the joint.
Fifth, it has been observed in practice that the distance between the metacarpals and the distal ulna-radius changes during flexion and extension of the hand. This change of distance results in an elliptical path being followed by the hand during its range of motion from flexion to extension. Furthermore, a differential motion has been observed during supination and pronation between the distal and proximal areas of the forearm. It is desirable in any dynamic splint design to mirror these kinematics so that binding of the appliance is prevented and a proper dorsal force can be applied by the splint appliance to resist volar glide.
Accordingly, what is needed is an improved appliance and method for resolving CTS. Such an appliance should desirably have the following characteristics:
1. The appliance must duplicate the stretching maneuver performed by a trained therapist to stretch the PTCL and collective volar carpal ligaments over time;
2. The appliance must be easily worn and removed by a patient with minimal or no training required for its use;
3. The appliance must not present pressure points to the patient or unduly irritate the skin;
4. The appliance must be easily worn during routine daily life with little or no interference with motion during supination and pronation or during manipulation of the fingers;
5. The appliance must both promote restoration of the carpal ligaments to their proper configuration as well as restore the proper cocontraction of the stabilizing flexor and extensor muscle groups against the carpal joint;
6. The appliance must be able to accommodate individuals having different forearm and wrist measurements; and,
7. The appliance must be not bind during supination and pronation of the forearm.
Other characteristics such as ease of manufacture and ease in cleaning the appliance are also desirable.
It is therefore an object of the present invention to provide an improved method and appliance for treating CTS.
It is another object of the invention to provide a method and appliance directed to the relief of pressure on the median nerve through the application of continuous, low intensity, volarly directed pressure to the hand in order to gradually lengthen the palmer transverse carpal ligament over time.
It is another object of the invention to provide a method and appliance which will restore the desired flexor-to-extensor ratio of force to the forearm of a person experiencing CTS.
It is a further object of the invention to provide a method and appliance which promotes restoration of the cocontractive forces of the flexor and extensor muscles on the carpal joint so as to allow the carpal ligaments to be properly stretched and/or contracted in order to achieve a normal carpal configuration.
Another object of the invention is to provide an appliance for the treatment of CTS which is comfortable to the person wearing the appliance.
Another object of the invention is to provide an appliance for the treatment of CTS which will not unduly interfere with the normal activities of daily living.
Another object of the invention is to provide an appliance which can be worn, adjustment, and removed by a patient with ordinary skill without adversely affecting the function of the appliance.
Another object of the invention is to provide an appliance which will not bind while the patient wearing the device performs supination or pronation movement and will continue to provide restorative force to the carpus during such movements.
Another object of the invention is to provide an appliance which is simple in construction.
Another object of the invention is to provide an appliance which can be easily adjusted to provide variable tension resisting dorsal movement of the hand.
Another object of the invention is to provide an appliance which accurately models the kinematics of the carpal/metacarpal complex in order to provide continuous tension resisting dorsal movement of the hand.
Other objects and advantages of the present invention will be set forth in part in the description and in the drawings which follow and, in part, will be obvious from the description or may be learned by practice of the invention.
To achieve the foregoing objects, and in accordance with the purpose of the invention as broadly described herein, the present invention provides methods and devices for a dynamic splint for relieving carpal tunnel syndrome. The method of the invention is implemented by means of a dynamic orthotic appliance designed to provide low level pressure on the PTCL over extended periods of time while at the same time allowing the user to execute the standard activities of daily living, as well as general activities particular to the user""s occupation, without interference from the orthotic. This is provided by a biasing component which models the movement of the carpal/metacarpal and distal forearm/carpal joints by employing a unique and innovative spring tensioning arrangement in the form of a plurality of coils to provide continuous, low pressure force opposing rotational movement of the hand about the carpus. The multiple coil arrangement mimics the lengthening and shortening of the distance between the metacarpals and the distal ulna-radius as the hand moves volarly and dorsally. By mimicking this lengthening and shortening which has been observed empirically, the biasing component accurately tracks hand movement. It can thus apply a continuous, low level force which accurately opposes rotational movement of the hand about the carpus to promote restoration of normal function to the carpus and forearm. The novel coils of the biasing component are positioned generally on the ulnar side of the carpus where they do not interfere with hand and arm movement during normal activities of daily living. They have a torquing end coupled to the hand and a supporting end which is coupled to the forearm. The biasing component has a rest, or zero force, position in which the hand is slightly and dorsally deviated at an angle from the plane formed by the ulna and radius of the forearm; any volar or dorsal movement from this angle is resisted by the biasing component.
In one embodiment of the invention, the dynamic orthotic appliance consists of three componentsxe2x80x94a biasing component, a forearm component, and a palmar component. The palmar component is positioned on the ulnar side of the hand and is designed to allow unobstructed flexion of the fingers and opposition of the thumb with the fingers; it couples the supporting end of the biasing component to the hand. The forearm component couples the supporting end of the biasing component to the forearm and maintains the biasing component in particular relationship and alignment with the ulnar aspect of the forearm and carpus during all normal movements. The forearm component allows supination and pronation of the forearm without binding of the appliance or obstructing free movement by creating two independently moving portions, which are generally associated with the distal and proximal aspects of the dorsal forearm to permit differential movement of portions of the forearm during supination and pronation. It places the biasing force on the ulnar side of the forearm and hand in order to avoid interference with normal movement. The three components are articulated in a novel manner which further avoids interference with the normal activities of daily living.
In an alternative embodiment, the device made according to the invention comprises a forearm component having two independently moving portions which are generally associated with the radial and ulnar aspects of the dorsal forearm to permit differential movement of portions of the forearm during supination and pronation. The force exerted by the biasing component can be controlled by a volar transverse strap.
In still another alternative embodiment, the device made according to the invention comprises a forearm component which has been reduced to a simple carpal cuff for stabilization of the biasing device and for providing a fulcrum about which the biasing component rotates. The level of force exerted by the biasing component can be controlled by a transverse strap connected to the supporting end of the biasing component and running volarly from the radial side to the ulnar side of the forearm to removably connect to the surface of the carpal cuff.
The present invention will now be described with reference to the following drawings, in which like reference numbers denote the same element throughout.